The present invention relates generally to metal roof panels, and more particularly, to metal roof panels with deformation-resistant ribs, and the method of making the same.
Metal roofs are a popular and practical alternative to conventional shingle roofs, due to their strength and durability, light weight and weather resistance. Metal roof panels can be made from a variety of metals including aluminum, galvanized steel (typically G-60 or G-90 steel), painted or coated steel, and stainless steel, and come in a variety of lengths and gauges. Roof panels typically have a series of elevated ridges (hereinafter “ribs”) separated by a series of lower laying “channels”. As shown in FIG. 1, panels are arranged on a roof so channels 20 and ribs 30 run substantially parallel to the slope of the roof. This allows water to run off of the roof, primarily along channels 20, in a substantially unimpeded path. As shown in FIG. 1, ribs 30 may have a flattened apex 32. The typical flattened apex is approximately ⅜″ wide. Alternatively, ribs 30 may be rounded, as shown in FIG. 2. Peaked apices are also conventional.
Roof panels are typically secured to the roof by screwing the panels onto the underlying substrate, although there is significant debate as to preferred screw placement: rib or channel. As depicted in FIG. 3, a roof panel secured by screw 40 at rib 30 is subjected to considerable “wind sway” or displacement of roof panel relative to underlying substrate 15. This wind sway is increased if screws aren't completely tightened. Unfortunately in an attempt to ensure screws are adequately tightened there is a tendency for installers to overtighten screws, which leads to deformation of the panels, as depicted in FIG. 1. Deformation of panels eventually leads to corrosion, rust, degradation, and failure of the panel.
Deformation of panels at the rib is a common problem because the ribs of conventional roof panels lack adequate structural strength. Said another way, conventional ribs “cave in” easily. This weakness is due to manufacturing limitations. Traditional panels are manufactured using a roll machine which bends metal at room temperature using a number of stations where fixed rollers both guide the metal and make the necessary bends. As the metal travels through the machine, each set of rollers bends the metal a little more than the previous station of rollers. However, these conventional sheet metal fabrication techniques can form only simple ribs with few angles because roof panels become unacceptably distorted during manufacturing when multiple manipulations are attempted. Very simply, introducing too many bends and angles introduces too many conflicting forces on the material, and the end result is a roof panel that is warped with ribs and channels that are not uniform and linear from one end of the panel to the other.
Curved (FIG. 2) and peaked or triangular ribs are fairly structurally strong and resistant to caving in, and can be manufactured using conventional techniques, but don't provide a flat surface against which the screw can lay flush. Said another way, the outer perimeter of screw 40 head isn't in contact with the surface of the rib 30, thereby potentially allowing the ingress of water, which leads to rust, degradation and failure. This is shown in FIG. 2.
The advantages of screwing the roof panel to the substrate at the channel are tainted by the simple fact that the channel is the water path, and water leaks through screw holes. While various implements such as gaskets may delay the entry of water into the screw holes, the inevitable degradation of materials and shifting of roof panels eventually leads to leaking. Leaking leads to corrosion of the roof panel, which leads to degradation, which leads to failure. Leaking also damages the underlying roof substrate and other building structures. For this reason it is also undesirable to screw roof panels to the underlying substrate along the roof panel's channel.
Thus there is a need for a roof panel that can be secured at the rib. It is desirable that this roof panel is strong enough to reasonably withstand wind sway and rib deformation. It is also desirable that the apex of the rib is sized and shaped to allow a standard screw and washer to lay flush. It is also desirable that the screw-apex interface is substantially impervious to water. It is also desirable that the roof panel is mass produced using improved manufacturing methods.